Global warming, climate sceptics keep staying, has stopped for the last 16 years or so. But nobody seems to have told the fish, who keep moving towards the poles as previously cool waters warm up.

Tropical species are increasingly moving into temperate seas, a bluefin tuna has been caught off Greenland, and Britons are facing having to change the way they eat fish and chips, all as a result of the climate change, say researchers. Marine ecologist, Dr. Adriana Vergés, of Australia's New South Wales University, says: “The magnitude of the change is so large that it is very obvious.”

The sceptics base their claim on just one measurement of warming, the temperature of air near the earth's surface , whose increase has indeed slowed down recently, though it has not stopped growing. This is the most obvious indicator to humanity, since it records the conditions in which we live, but it is only one of several used by scientists – and not the most important of them. Others include the amount of ice at the poles and in glacier which, in total, has been shrinking dramatically, and the continuing warming of the oceans – where almost all the extra heat ends up – which is particularly marked in some areas.

Sea temperatures around Britain, for example, have risen by 1.6 per cent – four times the global average – over the last quarter of century partly because they are relatively shallow, and partly because three of them (the Irish and North Seas and the English Channel) are partially enclosed. As a result, says Prof Callum Roberts of York University, “15 of the 36 species surveyed in the North East have shifted latitudes”, moving, on average, 300 km northwards.

Cod and haddock, for example, are now rarely found wild in British waters. They are being replaced by warmer water species like sea bass, hake, gurnard, red mullet and anchovies, while John Dory – once only found off Cornwall – has spread through the North Sea up to Scotland. Diets, however, have yet to change to match.

Even more dramatically, three bluefin tuna – a Mediterranean species – have been caught within 100 miles of the Arctic circle in what Prof Duncan MacKenzie of Denmark's National Institute of Aquatic Resources called “the first scientifically confirmed presence of the species in East Greenland waters in 342 years”.

He added that the catching tuna, which he thinks were part of a school of up to 100, “demonstrates that a large, highly mobile fish species is changing its range and distribution towards northern regions”.

Tropical fish are invading Japanese waters, the Eastern Mediterranean and even the US Atlantic seaboard, often stripping kelp forests bare. The emerald parrot fish has increased 22 fold in the northern Gulf of Mexico, while angel fish and Florida stone crab are appearing off the Carolinas. “People are seeing these fish all over the world in unexpected places”, says Prof. Ken Heck of the University of South Alabama. “I don't think there is any question that the movement of many tropical species is related to the warming of coastal waters.”